Technical Field
The present invention relates to a lock-up device for a torque converter, particularly to a lock-up device for a torque converter for transmitting a torque and absorbing and attenuating a torsional vibration.
Background Information
Torque converters are often equipped with a lock-up device for directly transmitting a torque from a front cover to a turbine. This type of lock-up device includes a piston, a drive plate, a plurality of coil springs, a driven plate and a spring holder (see Japan Laid-open Patent Application Publication No. 2011-252584).
In this type of lock-up device, a plurality of coil springs are disposed on the outer peripheral side, and likewise, a plurality of coil springs are disposed on the inner peripheral side. Additionally, small coil springs are respectively disposed in the inner peripheral parts of the plural coil springs disposed on the inner peripheral side, and each has a free length shorter than that of each coil spring disposed on the inner peripheral side. With the construction, multistage torsional characteristics are formed.